Ever watched a paint supplier do a custom tint for a factory color? It's definitely done by weight, at least at every shop I've been associated with. Put the mixing cup on the scale, and run the specified amount of base color or tint in, then move on to the next color. If 1/4 pint of a specific color is needed for a spot-paint job with a trim gun or an airbrush, no problem, and no waste. Those tinting colors are E$$PENSIVE!
Jerry
That's how my local PPG dealer does it. Watched them do it several times. The only time I've seen them do it differently was the last time I needed paint (got hit in the rear fender in the parking lot at work), had the correct code for the paint. After they mixed it, we went out to the truck to make sure it was right. Seems the color had faded a bit since the truck was originally painted. The guy mixing the paint took the cans of the appropriate toners and mixed it by eye right out in the lot. I was shocked at just how much PURPLE (??!! ) there is in that particular shade of blue.
However, while mixing the color was done by weight, mixing it to spray was done by volume. I got mixing cups from the paint dealer with the correct ratios marked on it, in this case, it's 8-1-1.
